(a) Field of the invention
The present invention relates to a process for the production of impure oxygen by air distillation in an apparatus for air distillation with a double column, the double column comprising a medium pressure column and a low pressure column.
The applications concerned by the invention are those which consume large quantities of impure oxygen. Processes for gasifying coal or petroleum residues, as well as processes for direct reduction-melting of iron ore may be mentioned.
(b) Description of Prior Art
In order to produce impure oxygen by air distillation, i.e. oxygen having a purity lower than 99.5% and generally lower than 98%, it is known that it is possible to decrease the energy expenditure by increasing the operating pressure of the double column, as long as the available energy can be used in the low pressure column in the form of pressure.
A known means to make use of this pressure, which is described for example in U.S. Pat. No. 4,224,045, consists in combining the air distillation apparatus with a gas turbine: the air to be separated is completely or partially withdrawn from the discharge of the compressor of this turbine, and the low pressure residual gas from the distillation apparatus is sent back to the gas turbine after compression, the impure oxygen and the nitrogen being sent to be used under the pressure of the column which produces them.
In this manner, the use of low pressure is completely justified and the energy used for separation is reduced.
The invention aims at still reducing the expenditure of energy which is required for the production of impure oxygen.